1. Field of the Invention
The present invention relates to a ceramic circuit substrate and manufacturing method thereof, more particularly, to a circuit substrate that has excellent thermal shock tolerance.
2. Description of the Related Art
A conventional method of manufacturing ceramic circuit substrate is shown in FIGS. 9, 10 and 11, wherein FIG. 9 is a top plan view, and FIGS. 10 and 11 are cross sectional views.
Referring now to FIG. 9, there are formed brazing material coated spots 2 that are printed in circular-shape dotted patterns, and partial full-coated sections 3 with the brazing material on the top surface of the ceramic substrate 1. The partial, fully-coated section 3 is provided for a semiconductor mounting section where e.g. a semiconductor chip is mounted. Furthermore, a brazing material fully-coated section 6 (shown in FIG. 10) is formed on the back surface of the ceramic circuit substrate 1.
Turning now to FIG. 10, an upper metal plate 4 is placed onto the brazing material coated spots 2 and partial fully-coated sections 3, a lower metal plate 5 is placed onto the brazing material fully-coated section 6, and then, forming a joint by heating in a furnace at 830° C.
After that, etching resist (not shown) is formed on the surface of upper metal plate 4 and on the surface of lower metal plate 5 respectively, and then, etch the upper metal plate 4, lower metal plate 5 and the brazing material coated spots 2 by an etchant using the etching resist as a mask. In this manner, unwanted parts of the upper metal plate 4, the lower metal plate 5 and the brazing material coated spots 2 are removed. After that, the etching resist is removed. As a result, circuit pattern section 7 composed of the upper metal plate is formed on the ceramic substrate 1; and the lower metal plate 5 which is provided for joining (soldering) with a heatsink and the like is formed on the opposite surface of the ceramic substrate 1; as shown in FIG. 11 (for example, see Japanese Patent Application Laid-open No. Hei 9-157055) . By adopting this construction, a ceramic circuit substrate, which has better property of thermal shock tolerance and tolerance to passage through a furnace as compared with the conventional circuit substrate, which has a fully jointed circuit pattern section, can be manufactured. In addition, as a conventional ceramic circuit substrate which has not improved thermal shock tolerance by the shape of brazing material, there exists an example in which brazing material is coated over the whole surface without the above-described brazing material coated spots 2.